http://www.6066gmcguy.org/SM420.htm toward the bottom of this page they list 5-speed info. there are about 15 different clark model#s, and only one lists an overdrive gear (.80). you can usually find the make and model of your trans by creeping under your rig with a flashlight, that's how I found the designation on the 5-speed spicer in my 68 C60. By the way, what kind of shape is that 350 in? I might be interested if you're swapping it out...
